In order to examine a target lesion in a lumen such as a blood vessel or a vascular channel, an ultrasonic catheter which transmits and receives ultrasonic waves to and from the target lesion is used. The ultrasonic catheter is provided with an imaging core which includes an oscillator unit for transmitting and receiving the ultrasonic waves and a drive shaft for rotating the oscillator unit, and a sheath which incorporates the imaging core and is inserted into the lumen. The imaging core can move in an axial direction in the sheath.
When the ultrasonic catheter is used, an introducer sheath for accessing the lumen is typically indwelled, and a guiding catheter is inserted into the lumen via the introducer sheath. Thereafter, a guide wire is inserted up to a targeted portion via the guiding catheter, and the ultrasonic catheter is inserted into a deeper portion than the target lesion along the guide wire. Then, only the imaging core is made to retreat such that the imaging core is arranged on a distal end side in the sheath, while the sheath is made to pass through the target lesion. Since the oscillator unit moves from the deeper portion and passes through the target lesion by causing only the imaging core to retreat, it is possible to observe ultrasonic images which are successively acquired before and after the target lesion and to create three-dimensional data with a shape of the blood vessel or the vascular channel.
In order to enable the imaging core to move in the axial direction in the sheath, an ultrasonic catheter disclosed in International Publication No. 1999/015078, for example, includes a nested structure which expands and contracts in the axial direction and is provided on a proximal end side, and the imaging core in the sheath is made to move in the axial direction with respect to the sheath by changing an entire length of a main body of the catheter.
In addition, the ultrasonic catheter disclosed in International Publication No. 1999/015078 includes a connection section which is provided between the sheath and the nested structure and can be connected and disconnected, and it is possible to pull out the imaging core from the main body of the catheter in accordance with a particular situation.
There is a case where the ultrasonic catheter, as disclosed in International Publication No. 1999/015078, is caught by a complicatedly curved blood vessel or a narrowed blood vessel or with a stent or the like which is embedded in a blood vessel, and is brought into a situation where it is difficult to pull out the ultrasonic catheter from the blood vessel. It is considered to facilitate easier pulling-out of the sheath by removing the imaging core from the sheath in such a case.
However, if pulling out the imaging core of the ultrasonic catheter disclosed in International Publication No. 1999/015078 is attempted, the connection section approaches a Y connector, which is connected on a proximal end side of the guiding catheter in a state where the ultrasonic catheter is inserted into the guiding catheter since the connection section is provided between the sheath and the nested structure. Since the guide wire also comes from the Y connector, there is a concern that the guide wire and the connection section may interfere with each other and it may become difficult to push the guide wire when the ultrasonic catheter is operated, which may deteriorate operability. Furthermore, since the connection section approaches the Y connector, there is a concern that blood flowing out from the connection section after the imaging core is extracted may be confused with blood flowing out from the Y connector, which may cause an erroneous operation. Furthermore, since the connection section approaches the Y connector, the blood flowing out from the connection section flows into a valve body, which is provided in the Y connector, from outside, which also may deteriorate operability.